1. Field of the Invention
The invention relates to an activation method for lithium hydride, and to a hydrogen generation method that uses lithium hydride that has been activated by the activation method.
2. Description of the Related Art
Researches and studies on fuel cells, a promising technology as a global warming countermeasure, are being actively conducted in recent years. A fuel cell is a device which causes an electrochemical reaction in a structural body that includes an electrolyte layer and a pair of electrodes, and which extracts electric energy that is generated by this electrochemical reaction. Among the fuel cells, a solid polymer type fuel cell (hereinafter, sometimes referred to as “PEFC”), which is utilized in various fields, such as household cogeneration systems, motor vehicles, etc., employs a hydrogen-containing gas and an oxygen-containing gas. Therefore, in achieving a practical application of the PEFC, it is essential to establish a hydrogen production technology and a hydrogen storage technology.
As hydrogen storage technologies proposed until now, there are known a form in which a hydrogen gas is compressed and stored in a high-pressure hydrogen tank, a form in which liquid hydrogen is stored in a liquid hydrogen tank, and a form in which a hydrogen storage material that has stored hydrogen is stored in a tank. However, in the form that uses a high-pressure hydrogen tank, the volume of the tank is large therefore making the size reduction is difficult, and there also be other problems, including a problem of being liable to greatly consuming pressurization energy if the hydrogen pressure is raised. Besides, in the form that uses a liquid hydrogen tank, since it is necessary to continue cooling the hydrogen to a very low temperature (−253° C. or lower), it is likely to consume energy at the time of storage of hydrogen; besides, there are other problems, including a problem of it being difficult to avoid the “boil-off” in which liquid hydrogen evaporates by the heat that flows in from outside the tank. Therefore, the form that uses a hydrogen storage material is drawing attention since this form requires less energy for the storage, and is free from concerns of the boil-off, and the like.
As a technology related to a hydrogen storage material, Japanese Patent Application Publication No. 2005-154232 (JP-A-2005-154232), for example, discloses a hydrogen storage material that is constructed of a metal hydride and ammonia, and that generates hydrogen through a reaction between the metal hydride and ammonia. Furthermore, Japanese Patent Application Publication No. 2005-154232 (JP-A-2005-154232) discloses a technology that uses a metal hydride that has been made into fine particles by a predetermined mechanical pulverization treatment. Moreover, Japanese Patent Application Publication No. 2005-154232 (JP-A-2005-154232) also discloses a technology related to a hydrogen generation method in which a metal hydride and ammonia are enclosed in a reaction vessel, and reacting the metal hydride and ammonia to generate hydrogen by stirring or pulverizing the metal hydride within the reaction vessel. Besides, Japanese Patent Application Publication No. 2006-205148 (JP-A-2006-205148) discloses a production method for a hydrogen storage material which includes a mechanical pulverization treatment process of mechanically pulverizing a mixed material that contains lithium nitride and an aluminum-base composite hydride that contains an alkali metal. Besides, Japanese Patent Application Publication No. 2006-247512 (JP-A-2006-247512) discloses a hydrogen storage material characterized by being constructed of a mixture that contains a metal element-supplying particle, and a lithium imide particle and/or a lithium nitride particle, and characterized in that the metal element-supplying particle, and the lithium imide particle and/or the lithium nitride particle in the state of mixture have been given mechanical energy.
According to the foregoing technology disclosed in Japanese Patent Application Publication No. 2005-154232 (JP-A-2005-154232), Japanese Patent Application Publication No. 2006-205148 (JP-A-2006-205148), and Japanese Patent Application Publication No. 2006-247512 (JP-A-2006-247512), since the hydrogen storage material employed has been subjected to a mechanical pulverization treatment, it becomes possible to improve the utilization rate (rate of reaction) of the hydrogen storage materials used for the hydrogen generation reaction, in comparison with the case where the hydrogen storage material is not subjected to the mechanical pulverization treatment. Besides, according to the technology disclosed in Japanese Patent Application Publication No. 2005-154232 (JP-A-2005-154232) in which a metal hydride and ammonia reacted while the metal hydride is being pulverized, it becomes possible to increase the efficiency in the generation of hydrogen. However, if a vessel containing the metal hydride and ammonia is mounted in a fuel cell vehicle and the hydrogen generated while the metal hydride is being pulverized is supplied to the fuel cell, there arises a problem of it becoming difficult to prevent the pulverized metal hydride from flowing into the fuel cell over a long duration and therefore it being likely that a trouble, such as hydrogen leakage, malfunction, etc., will occur. Therefore, considering the application to fuel cell vehicles, it becomes necessary to increase the efficiency in the generation of hydrogen without performing a mechanical pulverization treatment during the hydrogen generation reaction. In order to accomplish this task, it is desirable to develop a technology that activates the hydrogen storage material into a form that is capable of increasing the utilization rate (reaction rate) of the hydrogen generation reaction. However, there is a problem of it being difficult to sufficiently activate the hydrogen storage material even by a combination of the technologies disclosed in Japanese Patent Application Publication No. 2005-154232 (JP-A-2005-154232), Japanese Patent Application Publication No. 2006-205148 (JP-A-2006-205148), and Japanese Patent Application Publication No. 2006-247512 (JP-A-2006-247512).